The present invention relates to photographic equipment and, more particularly, to exposure setting devices for adjusting exposure depending upon the intensity of illumination of an object being photographed and the sensitivity of the film used.
The proposed exposure setting device is intended for setting a required time of exposure, warning about unfavorable conditions for photography and adjusting the power source voltage to ensure fixed exposure time values.
The invention is utilised for automatic exposure time or diaphragm setting and as an electronic release device for all types of photographic equipment. In addition, the device of the present invention may be used as a threshold element in timers, etc.
Most conventional exposure setting devices intended for automatic exposure and diaphragm setting comprise, as a main unit, an integrating timing RC circuit with variable parameters, wherein the variable parameter is a light-sensitive element, for example, a photoresistor, of a threshold unit, an actuator and a signal unit. The light flux reflected from an object being photographed is incident on the light-sensitive element and alters its parameters. A change in these parameters brings about a change in the time constant of the integrating RC circuit. Depending upon the latter's value, the threshold unit sets the exposure time or diaphragm and correspondingly controls the actuator. The signal unit is intended for indicating the observation conditions.
The known exposure setting devices are intended, in the main, only for a specific type of equipment. The electrical circuitry of such devices incorporates in most cases p-n-p and n-p-n semiconductor elements; high input resistancies are ensured through the use of field-effect transistors or metal-oxide-semiconductor structures, which accounts for an extremely complicated process of producing a circuit in a single crystal.
In order to simplify the electric circuit of an exposure setting device, many companies make use of a great number of mechanical contacts, which reduces the reliability of the photographic equipment as a whole. In many types of cameras accurate indication of conditions for photography is ensured with the aid of pointer indicators.
In addition, conventional devices lack means for stabilizing the exposure time duration depending upon variations in the supply voltage.
The foregoing considerations dictate the necessity of evolving an all-purpose electronic microcircuit for exposure setting which is applicable in all types of photographic equipment.